Support for @template-contravariant tag

[oprypkhantc]

Feature request

PHPStan currently allows two types of variance for template types in class-likes: @template (invariant) and @template-covariant (covariant). PHPStan also internally supports the third type: contravariant, but lacks support for specifying it for class-likes with a PHPDoc.

This is, however, sometimes useful:

/**
 * @template-contravariant T
 */
interface Comparator
{
    /**
      * @param T $e1
      * @param T $e2
      */
    public function compare($e1, $e2): int;
}

The implementation should theoretically be trivial: add support for @template-contravariant tag in phpdoc-parser, then correctly parse those tags into respective variance on phpstan side. As far as I understand, the support has been there internally for a long time already.

We'll also need to modify https://github.com/phpstan/phpstan-src/blob/f8be122188aa6721cec9872bd61676ee150a5311/src/Rules/Generics/VarianceCheck.php#L53 to check contravariance in parameters.

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[ondrejmirtes]

What's the use-case? Your example doesn't imply anything about the need for contravariant.

[oprypkhantc]

I'll give a different example: https://phpstan.org/r/f19ee206-09de-4b84-968d-5d2a74373228

[ondrejmirtes]

It's not hard to add support for this.

1. https://github.com/phpstan/phpstan-src/blob/1.7.x/src/Type/Generic/TemplateTypeVariance.php is already ready.
2. This needs a small modification: https://github.com/phpstan/phpstan-src/blob/ec1e8e7d6749cd839d7b5399134c1069cd637dcb/src/PhpDoc/PhpDocNodeResolver.php#L256-L262
3. This needs a small modification: https://github.com/phpstan/phpdoc-parser/blob/25ddf938d8f71485ab9630428920ea8474504db4/src/Parser/PhpDocParser.php#L175-L182
4. This would have to be updated so that it complains about contravariant T in a return type position: https://github.com/phpstan/phpstan-src/blob/ec1e8e7d6749cd839d7b5399134c1069cd637dcb/src/Rules/Generics/VarianceCheck.php#L62-L84

[dktapps]

Related issue (probably dupe): #3960

[ondrejmirtes]

Yes, please follow the original issue.

[github-actions]

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